Method of and means for casting metals under the influence of vacuum



Oct. 13, 1959 Filed March 3, 1958 w. G. WILKIN METHOD OF AND MEANS FORCASTING METALS UNDER THE INFLUENCE OF VACUUM TSheets-Sheet 1 InventorWILLIAM G. Wuxms J agys.

1959 w. G. WILKINS 2,903,054

METHOD OF AND MEANS FOR CASTING METALS UNDER THE INFLUENCE OF VACUUMFiled March :5, 1958 7 Sheets-Sheet 2 I 1i J! Jr J I, 1F JV Jr J I M it1? JF l JF'Jl '1 IF I J[ J[ JF J] Il 41F ll JP J l y Q O 2' InventorWILLIAM G. WILKINS O 2 @05 w ag Oct. 13, 1959 w, w s 2,908,054

METHOD OF AND MEANS FOR CASTING METALS UNDER 'THE INFLUENCE OF VACUUMFiled March 3,. 1958 7 Sheets-Sheet 3 wmmnl A g ,7

entor WILL G. WILKINS Oct. 13, 1959 w, w K s 2,908,054

METHOD OF AND MEANS FOR CASTING METALS UNDER THE INFLUENCE OF VACUUMFiled March 3, 1958 7 Sheets-Sheet 4 Inventor WILLIAM G. WILKINS b,:..1..-.,@;;w ;m J

Oct. 13, 1959 'w.,c-z. WILKINS 2,908,054

ma'mon or AND. MEANS FOR CASTING METALS UNDER THE INFLUENCE OF? VACUUM IFiled March :5, 195a 7 Sheets-Sheet 5' -m, Gwfiwm 0515 N 6% days 1959,w. e. WILKINS 2,903,054

- METHOD OF AND MEANS FOR CASTING METALS UNDER THE INFLUENCE OF VACUUMFiled March :5. 1958 7 Sheets-Sheet 6 jae/aay 13m, 625m. #M f fa @zzawzmOct. 13, 1959 w, w 2,908,054

, METHOD OF AND MEANS FOR TING METALS UNDER THE INFLUENCE VACUUM FiledMarch 3, 1958 7 Sheets-Sheet 7 "ISO H56 I v United States Patent 9METHOD OF AND MEANS FOR CASTING METALS UNDER THE INFLUENCE OF VACUUMWilliam G. Wilkins, Chicago, Ill., assignor to Universal CastingsCorporation, Chicago, Ill., a corporation of Illinois Application March3, 1958, Serial No. 712,182

Claims. (Cl. 22-73) The present invention relates generally to casting,especially of metals, and more particularly to a new and improved methodof casting and apparatus by means of which the method can be practiced.

The invention finds particular, though by no means exclusive, utility inprecision casting as is frequently employed in forming devices embodyingcored openings of arcuate or irregular shape, those having extremelythinwalled portions, and those from which no substantial metal removalby machining is to be subsequently efiected. In conventional practicethe material to be cast is first heated to a temperature well above itsmelting point and is introduced into a mold by way of a sprue openingwhich is connected to the mold cavity by Way of a runner,

provision being made to vent the mold cavity and to incorporate risersand shrinkheads to insure filling of the cavity and by providingadditional metal to compensate for shrinkage during cooling. By way ofexample, in the casting of aluminum the temperature is initially raisedto approximately 1600 F. so as to obtain desired fluidity. Thisextremely high temperature has been found necessary in conventionalpractice where castings having thin- Walled sections are to be made. Inthe casting of such devices by conventional methods only about one-thirdof the metal poured is utilized to form the casting per se, theremainder going into the runners, risers, shrinkheads, and sprueopenings. Furthermore, under conventional practice at extremely hightemperatures required, it has been found that up to 70% of the castingsso formed had to be scrapped because of incomplete filling of the moldcavities and because of high porosity which results in poor physicalproperties, primarily with regard to tensile strength. Investigationshave led to the belief that as a result of the requisite hightemperature required to obtain the required fluidity, there is asubstantial increase both in the occlusion of gases and-in oxideformation. X-ray pictures indicate such porosity as literally hundredsof interstices of voids. Further, the incomplete formation of the edgesof remote portions of castings made under conventional practice isbelieved to be caused by the incomplete removal of air and other gasesfrom remote portions of the mold cavity.

Accordingly, it is a general object of the present invention to providean improved method of casting'by means of which the above-mentioneddifliculties are substantially eliminated.

rapid and economical practice, and whereby the initial temperature towhich the metal to be cast need by raised is only slightly above itsmelting point so as to achieve the 7 It is a related object to provide amethod of casting metals permitting" of more complete filling of themold cavity with the molten cast- 2,%8,54 Patented Oct. 13, 1959castings are obtained.

Another and equally important object of the invention is to provideapparatus by means of which the new and improved method of casting canbe practiced for producing ferrous as well as non-ferrous metalcastings.

The objects or" the invention thus generally set forth, together withother objects and ancillary advantages, will become apparent as thefollowing description proceeds taken in conjunction with theaccompanying drawings, in which:

Figure 1 is an elevation of a casting apparatus embodying features ofthe present invention and by means of which the novel method can bepracticed.

Fig. 2 is a top plan view of the apparatus shown in Fig. l.

Fig. 3 is a vertical section taken in ofiset planes along the line 3-3in Fig. 2.

Fig. 4 is a bottom plan view of the top plate of the apparatus shown inthe preceding figures.

Fig. 5 is a bottom plan view of a typical top mold' section.

Figs- 6 and 7 are perspective views of castings of complex form whichhavebeen successfully made through the practice of the instantinvention.

Figs. 8 and 9 are central vertical sections taken through a casting likethat shown in Fig. 7, the former being made by conventional practice andthe latter according to the present invention. These figures comprisereproductions of actual photomicrographs.

Figs. 10 and 11 are vertical sectional views similar to Fig. 3 butillustrating modified forms of apparatus embodying features of thepresent invention.

Figs. 12 and 13 are elevation and plan views, respectively, of a furthermodified form of the apparatus as employed in casting metals having anextremely high melting point, such as ferrous metals.

Figs. 14 and 15 are elevation and plan views, respectively, of yetanother modified form of apparatus embodying features of the presentinvention.

Fig. 16 is a bottom plan view of the vacuum plateshown in Figs. 12, 13,14 and 15.

Fig. 17 is an enlarged vertical sectional view along the line 1717 inFig. 12.

Fig. 18 is a fragmentary perspective view looking upwardly at theunderside of a modified form of clamping preferred embodiments, but itis to be understood that is is not thereby intended to limit theinvention to the specific forms disclosed, but it is intended to coverall modifications and alternative constructions falling within thespirit and scope of the invention as expressed in the appended claims.

Referring more palticularly to the drawings there is shown a castingapparatus embodying features of the present invention which comprisesgenerally a mold 20, including an upper section 2011 and a lower section20b, mounted between-a bottom supporting plate '22 and a top clampingplate 24. As shown, the two mold sections are arranged to meet in a flatparting plane as indicated at 25, and may be equipped with positioningdowels 25 (Figs. 3 and 5). The mold sections have formed in theircontiguous faces appropriate recesses which define tion as at" 39' toany suitable means (not shown) for raising and lowering, the upper plateinto and out of engagement with the top mold section 20a. The top plateh'asa collared'opening 40' therein which is adapted to receive anannular ceramic insert 42 and hold same in registry with the sprueopening 32 in the top mold section 20a whereby to direct the moltenmaterial to be cast from a ladle or the like (not'shown) into the mold20.

To direct a ladle or the like into proper position for pouring itscontents into the open endof the ceramic insert 42 in the top plate 24,a V-shaped guide 44 is provide'd. The guide, as shown, is formed ofordinary angle-iron sections 44a held in rigid relation by means of' across strip 44b welded thereto.

The guide 44 is mounted on the top plate'24 over the spider 38, in sucha position that its legs extend outwardly to include therebetween thecollared top plate opening 40'.

The present invention contemplates casting under the influence of vacuumindirectly applied to the mold cavity. This is to the end that air andother gases are positively removed from the cavity and the moltenmaterial to be cast is drawn from the sprue opening and runner into thecavity against the walls thereof even in the most remote regions of thecavity. More particularly, it is content plated that evacuation of themold cavity is to be efiected through the walls of the mold that definethe cavity.

Thus there is a complete removal of air and the like from the cavity anda drawing of the material being cast directly. against the cavity wallswhere it is held until solidification. Itwill be seen, therefore, thatthe cavity is qui'clsly'filled and complete filling is assured with theresult that the necessary initial temperature of the casting materialneed be only slightly. above the meltingpoint thereof. ducedeven in suchfar reaches of a complex cavity as define knife-thin cast sections. As aresult of the lower casting temperature porosity is minimized andshrinkage is substantially reduced. These'things both contributemarkedlyto a high yield percentage of good sound castings for thequantity of castingmarterial poured.

In carrying out the invention molds formed of porous ceramic materialare utilized and the'cavities therein are subjected to an indirectlyapplied vacuum. That is to say, vacuum is applied exteriorly of themold, and the cavities therein are evacuated through the walls thereofby virtue of the porous character of the material of which the moldsections are formed. This positively and completely evacuates the moldcavity, eliminates the time and necessity for air or the like trapped inremote regions thereof to be absorbedby the mold, and the moltenmaterial introduced into the cavity is drawn quickly against the wallsthereofr In the form of the invention illustrated in Figs. 1-5,.

inclusive, of the drawings, the mold 20 is formed of a One 65 gredientssubstantially in the following proportions by porous'ceramic materialsuch as molders plaster. suitable form of such plaster comprises thefollowing in- For use the plaster is mixed with water in adequate amountto obtain the desired molding consistency. This plaster will set in acomparatively short time and is in-.

Further, completely formed castings are proplaced in superimposedrelation on the bottom supporting;

. 4 hibited against cracking. Subsequent to the setting of the plaster,green mold sections a and 2% are removed from their molding boxes andare heated in a suitable oven to a suitable temperature for a sufficienttime to cure them and to remove a cavity forming material if such wasused.

The mold sections 20a and 2012, thus formed, are then plate 22iandithetop plate 24-is lowered into clamping engagement therewith.

In the present instance, the cavities 28' of the. mold '20 are evacuatedby subjecting the mold to a vacuum applied to the top surface of themold section 20a so as to withdraiw air and other gases from thecavities-28 and to draw the molten material being cast against thecavity walls. As shown, the top plate 24 is formed Withawafile-iron-like lower surface so as to define a pattern ofinterconnected passages 46 over substantially theentire upperfsurfaceof-the. upper mold section 20a; To provide communication between theseinterconnected passages and a vacuum pump, the top plateis' provided:

with an opening 47which is suitably adapted. for the reception of afitting '48 for accommodating a vacuum.

hose 49.

The wafile-iron-like formation of. the underside of the top plate 24 "ispreferable to a singleuniform cavity formation, which might be used,because the topplatc serves. not only as the medium for the application.of

'vacuum to the mold 20, but additionally. through theoperation of:tlieolamping means, includingthe spider 38, to. apply a clampin'gforceto the mold 2.0 so as to main- The wafiie-iron-like formation providesfeet or pads 50 distributed over the entire top surface of the top moldsection 20aso' as to.

uniformly; apply the clamping pressure thereto. Thus, the.mol-drsections 20a and 2% are firmly held together so as tominirriize.leakage into the mold cavities 28 between the mold sections20a and 20b along the parting plane 25.

To further insure the application ofvacuum to the mold cavities 28 andto further minimize leakage top plate 241s equipped with suitable knifeedges which are'adapted to bite. into the relatively soft upper surfaceof the top mold section 20a.

for the reception of knife-edged inserts 51. The inserts are suitablysized for press-fitting into the grooved under:

surface. oftop plate 24 and project downwardly there-f by way'of theporous walls of the mold 20. This particular construction isadvantageous, too, in that it readily" perm-its replacement of theknife-edged inserts-51 and 52 ifthey should becomedull or damaged.

From the foregoing it will be seen that when molten metal or othermaterial is poured into the funnelled open end of the ceramic liner. 42which is received within the'collared opening 40 inthe top clampingplate 24 and into the sprue opening 32 in the top mold section, itisimmediately drawn along the runner 30 into the mold cavities 28 andagainst the walls. of thelatter by the-vacuum indirectly-applied theretoto the top mold section 20a:

In Figs; 6-9, inclusive, there of. impellers, generally denoted 60'and62, as illustrative of the type of complex precision cast products.which have been successfully made by the practice ofxthe'presentinvention. Both of these deviceszare'of' a form makbe precisionmadebecause they areintended for rotationat. extremely high spedsthereby'requiringgthatlhey; be

7 Thus, adjacent the marginal edges of the underside thereof, the topplate 24 is suitably grooved are shown: two. forms.

dynamically balanced. Figures 8 and 9 are central longitudinal sectionstaken through impellers of the type shown in Fig. 7, and comprisereproductions of actual photomicrographs. The impeller section shown inFig. 8 was made by conventional practice wherein the aluminum alloy ofwhich the device was fabricated was heated to an initial temperature ofsubstantially 1600 F. introduced into a mold and permitted to cool. Thesection shown in Fig. 9 was made by the practice of the presentinvention and with aluminum alloy from the same original melt but heatedto any initial temperature of only 1275 F. and introduced into apparatussuch as that herein before described and shown in Figs. 1-5. Therelatively high porous character of the casting section shown in Fig. 8is at once apparent. In Fig. 9, however, the casting section there shownis homogeneous and substantially free of voids.

In Fig. 10 there is shown a slightly modified form of the apparatusembodying features of the present invention. Where practical, identicalreference characters have been utilized in the description of thesemodified forms as have been utilized in connection with the form of theinvention shown in Figs. 1-5, inclusive. In this device the mold 20comprising the mold sections 20a and 20b and the top clamping plate 24are identical with the preceding form. In this form, however, not

only is avacuum indirectly applied to the mold cavities- 28 by directlyapplying the same to the top surface of the upper mold section 20a, butin addition a vacuum is applied uniformly over the bottom surface of thebottom mold section 2012. Thus the device shown in Fig. 10 is equippedwith a bottom supporting plate 26A which, like the top plate 24, has theupper surface thereof, which is engageable with the mold 20, made ofwaffle-iron-like form so as to provide a pattern of interconnectedspaces or passages 66 and suitable supporting pads 68. a suitable vacuumhose connection 70 which communicates with the system of passages 66 byway of a port 71 formed in the bottom plate 26A in the outer end ofwhich the hose connection 70 is received. This form of the inventiontends to more quickly exhaust the mold cavities 28 and to draw the metalfrom the sprue opening 32 runner 30 and mold cavities 28 at a somewhatgreater rate. It will be appreciated of course that shortly after themolten material to be cast is introduced into the mold the lowermostsurfaces of the mold cavities, the sprue opening 32 and the runner 30are covered by the molten material which substantially closes oif theoutflow of air therefrom. This construction, however, reduces the timerequired to fill the mold completely by a substantial amount. Not onlyis the mold evacuated more quickly by way of the top section 20a and,initially, in conjunction with the evacuation by way of the bottomplate, but several additional advantages come about by thisconstruction. Among the advantages is the fact that both mold sections20a are held firmly against the contiguous plates thereby permitting ofready separation of the two mold sections by the action of atmosphericpressure on the adjacent sides of the sections as a result of evacuatingthe spaces behind the same. Of course, since the molten material to becast covers the lowermost interior surfaces of the mold cavities 28 andthe runner 30, the vacuum indirectly applied to the bottom mold section2% has relatively little effect on the further exacuation of the moldcavities because the pores of the material of which the lower moldsection is formed are in effect sealed off by the molten material.However, some evacuation is had by way of the interconnected poresaround these surfaces. Thus, the hold-down action on the bottom moldsection and the additional exhaust of the interior of the mold makesthis construction not only practical but desirable as well.

The form of the invention shown in Fig. 11 includes The bottom plate 26Ais equipped with a mold 20B comprising upper and lower mold sectionsdefining mold cavities 28B disposed between a top clamping plate 243 anda lower supporting plate 26B. In this form of the invention, however,the molten material to be cast is introduced in the interior of the mold20B by way of a. sprue opening 32B formed .in the lower section of themold 20B'which is in registry with an opening 75 formed in thesupporting plate 26B, the latter being lined with a suitable ceramicinsert 76. The mold cavities 28B are connected with the opening '75 inthe bottom section of the mold 20B by Way of a runner 30B.

In this instance it is intended that the molten material to be cast bedrawn upwardly through the opening '76 in the supporting plate 26B andin the bottom section of the mold 20B and thence by way of the runner30B into the mold cavities 28B by means of vacuum indirectly applied tothe top section of the mold 20B. Thus the clamping plate 24B is alsowaffie-iro'n-like form, providing a pattern of-interconnected passages79 which serve to apply a vacuum substantially uniformly over the uppersurface of the top section of the mold 20B. The passages 79 areconnected to suitable evacuation apparatus (not shown) by way of anopening 80 formed in the clamping plate 24B which is adapted to receivea vacuum hose connection 81.

While in the illustrative embodiments molds of general rectangularfiguration have been shown for purposes of illustration, it will bereadily appreciated that molds may be made of any desired shape-square,rectangular, oval, etc.and the upper and lower clamping plates in suchcases will be fashioned to conform thereto. In each instance, along theouter marginal edges of the clamping and supporting plates and about thesprue openings in the molds there is provided a sharp depending flangeor knife-edge 51B and 52B adapted to bite quite deeply into thecontiguous mold surfaces so that when the mold is clamped therebetween atight seal is provided between the contiguous plate and mold surfacesthereby insuring that the inflowing air into the plate passages iseffected by Way of the pores of the mold section. In this way, with theplates so designed that vacuum is applied substantially uniformly overthe entire contiguous mold section surface, the mold designer need havelittle concern when planning the mold as to location of the moldcavities so long as they are well within the dimensional limits of themold.

As soon as the sprue opening in the mold is filled with the moltenmaterial to be cast which obviously occurs in an extremely short time,the application of vacuum to the mold insures an all-over pull on themold cavities with the result that residual air and gases in thecavities are withdrawn, and any gases that might be occluded in themolten material to be cast, as well, are withdrawn. Furthermore, thenecessity for the provision of large shrinkheads in the top mold sectionis eliminated, and shrinkage upon cooling can be accommodated byrelatively smaller shrink reservoirs located in the bottom mold section.Furthermore, the volume of the runners can be substantially reduced.Thus, with the smaller shrink requirement and the smaller runner volumea substantially larger casting yield for the quantity of melt pouredobtains.

Referring particularly to the form of the invention shown in Fig. 11 ofthe drawings, wherein the molten material to be cast is suppliedupwardly to the bottom mold section 26B to the runner 30B, thence to thecavities 28B by the action of atmospheric pressure as a result of evacuation of the interior of the mold, turbulance in the melt issubstantially minimized, particularly as compared to that produced inthe case of introduction of melt into a mold by direct pouring and underconventional casting methods.

The forms of the invention shown in Figs. 12-17, inclusive, compriseapplications specially adapted for the casting offerrous metals whichhave an extremely high; melting pointas compared withaluminum, forexample.

Such materials include both alloy and carbon steels, which metals mustbe raised 'toZSOO F." and upwards before melting occurs.

mounted iii depending relation from .the horizontal frame member 85 anda. piston :90 reciprocable Withinthecylinder: by. pressure fluidalternately entering-and leaving thecylinder throughopenings91z.Aclamping frame includingzvertically-disposed tie.-rods-92:and parallelupper andlower cross bars 94, .95, respectively, is rigidly connectedat. thelower cross bare 95 to a: piston rod 96. extending.

downwardly from thespis'torr and cylinder 89, 90. As. will be seen; thetie rods 92 pass through suitable openings in thehorizontal framemember. 85 so that the upper crossbar 94 is spaced a distance: above themember 85 sufficient, to accommodate the mold 86'therebetween. In thisway the clamping; frame is; adapted for up and down movement withrespect to the mold86 as the piston 90 reciprocably traverses thecylinder 89.

In carrying out the invention themold 86, formed of suitable porousceramic material, and the cavities 98 therein (Fig. 17) are subjectedtoan indirectly applied vacuum by means of an upwardly facing vacuumplate 99 disposed in mold supporting relation on the horizontal framemember 85. As will be seen, the mold 86 is se curely gripped between thevacuum plate 99 and the upper cross bar 94;when-the metal tobe cast isreadyfor pouring.

Because the'hereinbefore described plaster-type moldmaterial' undergoesspalling in the melting temperature range of carbonand alloy steels,e.g. 2500 F. and up, it is necessary to provide an investment materialwhich has the requisite high temperature refractory qualities and-yet iscapable of being formed into a porous mold. One. form of such aninvestment material comprises the following ingredients substantially inthe indicated portions by weight:

p Percent Powdered silica 1 40 Ethyl silicate 33 China clay -1 27 Foruse the above ingredients are mixed with water in an adequate amount toobtain the desired molding consistency. A characteristic of this moldingmaterial, however, is that after being mixed it must be heated to atemperature of about 2000 F. before setting up to permit handling. Y

Accordingly, provision is made for sustaining the form of the moldduring curing thereof by completely encasing the investment materialwithin a shell or sheath 100 which becomes a permanent part of the mold.With particular reference to Figs. '12 and 17, it will be seen that theillustrative shell 100 takes the formof an open end metal cylinder into,which the investment material is poured after mixing and which serves tocompletely enclose the mold material during both curing thereof andsubsequent casting therein of molten metal; Thus, an empty cylinder 100may be placed on a suitable flat base (notshown) and filled with'theformable wet investment material there being properly placed within thecylinder a suitablecavity forming materialor pattern. Insertion of thefilled, cylinderv inanoven (not shown) maintained at approXimately.-2000F. foriagsuitable time to curejthe mold material and to melt the cavityforming material if such was usedthenimparts a permanent setzto. themold.

The 1 sheathed mold -.86' is then in condition t o ,be clamped in"positiomon the vacuumplate- 99 for 'admissionfthereto ofamolten metal.

Interposed between. the a topof the mold: 86 and the upper cross 'bar 94is a top mold plate 10I having an open- 1 ing: 102 in registry with themold sprue; opening I 104" whereby-4o dir ect the'molten metal to becast from a lippour ladle or the like (not shown) into the molds Thus,-th e cavities 98 0f the mold 86' are evacuated bysubjectingthe mold toavacuum applied to the plate 99 through asuitab'levacrium connection ltlscommunicat-p ing with avacuum source (not shown); Asbefore, the.vacuum:actionwithdrawsair and:other gases from the.

cavities-98 and also draws. the molten material being cast.

against the cavity. walls.

The vacuum plate 99 shownis very similar: to the plates. hereinbeforedescribed; except that; the plate shown in, this embodiment is shaped asa-circular disc. to conform.

to the cylindrical mold shape. From Figs; 16 and 17,-it

is seen that =the;plate 99 is provided with awafile-iron-likef upper:surface ltld so. astodefine a pattern'ofv intercon-- nectedxciroular.andstraight passages 108coverysubstantiallythe entire surfaceof'themold. Communication be;-

tweenthese inner passages 108; and the. vacuurmconnection "-is.-eifectedthrough an opening 109 providedEin" themold cavities 98'andforminimizing. dissipation of the.

vacuumforces through leakage. the vacuum plate 99-isprovided. with anupstanding circular knife edge 111" adapted to bite intothe relativelysoft lower surface of the mold'86r. The knife edge 111fits tightly intoanappropriate' groove providedinthe plate so as to be easily re-,placed'when dull.- Thus, any inflow of air into the interof theporousyconnectedpassages 108 must be by 'way walls of the'mold 86.

A' preferred form ofthe invention includes an array of closely spacedperforations 113 provided over substantially'the entire surface of themold shell 100- in order to permit air to be drawn-therethroughandthrough the porous investment material to thereby create, a chillingaction; on the castings within the mold. It is found that such anarrangement effects a higher rate of coolingofr thecastings than thatnormally attainable so as to produceafinely grained casting producthaving uniform and highly desirable physical characteristics.

The embodiment ,ofthe invention illustrated in Figs. 14

and 15 is similar' to that shown in Figs. 1213 except that the sheathedmold86'a is clamped tothe angularly disposed outlet or month 114 of arockable furnace 115,

preferably of arr-electric type, which-may be tilted to fill the moldwith molten metal. Thus, as shown in the draw-- ings, a frame 116 forsupporting the tiltable furnace isprovided and suitable means includinga gearmotor 118 and'cradlemember 119-are used for rocking the furnacebetweenanupright and a tilted position (shown in phantom in Fig; 14).

The, furnace 115- ispivotally supported on the frame 116, by. arms 120andtherocking cradle 119 is pivotally' connected to the furnace atsomepoint 121 above the axis. of the supporting arms. Rotative motion isimparted to.

cylinder 126 is rigidly connected to the upper frame bar V 125,:independing relationthereto and a reciprocable piston; 126? disposed inthe cylinder carriesa vaccum plate, 99a on the lower end of a piston rod129. The pressure. fluid; operated, piston and cylinder. arrangement 128, 1 26 accordingly moves the vacuum plate 99a toward or away from thefurnace mouth 114, as desired, to clamp or release the mold 86a.

The mold 86a employed is identical to that used in the apparatus ofFigs. 12 and 13, as shown in Figs. 16 and 17, having a sprue opening(not shown) positioned contiguous to the furnace mouth 114. Acylindrical shell 100a surrounds the investment material forming themold, the shell being preferably formed with perforations 113a tofacilitate cooling of the castings after the molten metal has beenpoured.

As will be observed, the ends of the mold 86a are appropriately sealedfrom leakage of air or molten metal. Thus, it is preferred to interposea gasket 130 between one end of the mold and the furnace mouth 114.Likewise the other end of the mold is sealed by the provision on theoperating surface of thevacuum plate of a circular raised knife edgeadaptable to assume a biting relationship with the mold material.

Operation of the illustrative apparatus of Figs. 14 and 15 is effectedby melting in the electric furnace 115 a metal charge to be cast. Withthe mold 86a clamped firmly to the furnace mouth 114 and when the metalis transformed into molten condition, the furnace 115 is rocked by meansof the gearmotor 118 and cradle 119 from theupright to the tiltedposition. Vacuum may be applied to the vacuum plate 99a simultaneouslywith the flow of melt from the furnace 115 into the mold 86a, or thevacuum may be applied whenever desired.

The'method and apparatus hereinbefore described have been placed in useunder actual production conditions. Through the utilization thereof ithas been found that not only does a substantially higher percentage ofyield obtain, but additionally the castings so formed do in fact possessimproved physical properties. Further, it. has been found that there aresubstantially no rejects when the molds themselves are properly formed.Precision castings have been successfully made under productionconditions and speeds with extremely thin-Walled sections to aspecification accuracy of .005 of an inch.

There is shown in Figs. 1820 a modified form of clamping plate which mayalso be used in any of the illustrative casting apparatuses describedherein. An illustrative vacuum clamping plate 150 is there shown whichis similar in overall shape and construction to the clamping plates 24,24B and 26A described above. As shown the plate 150 comprises the topplate for use in one of the illustrative casting. apparatuses and isprovided with a wafile-iron-like formation of feet or pads 152distributed over its entire undersurface.

As before, the spaced feet 152 uniformly distribute clamping pressureover the surface of a porous upper mold section 154 of any of the typesdescribed heretofore and define therebetween a pattern of interconnectedpassages 156 over substantially the entire upper surface of themoldsection. Evacuation of the mold cavities is accomplished by subjectingthe interconnected passages 156 to a vacuum whereby air, occluded gases,and the like are withdrawn through the porous walls of the mold. As inthe case of the vacuum clamping plates described above, theplate 150 ispreferably provided about the periphery of its clamping surface withsuitable knife edges 158 which are adapted to bite into the relativelysoft upper surface of the mold and thereby minimize leakage ordissipation of vacuum.

The improvement disclosed here and shown in Figs. 18-20 of the drawingsconcerns the opening 160 which is provided in the plate 150 to providecommunication between theinterconnected passages 156 and a vacuum pump(not shown). In an arrangement similar to those disclosed above asconcerns the vacuum plates 24, 24B, and 26A, connection between theplate opening 160 and the vacuum pump is accomplished using a suitablevacuum hose (not shown) which'is secured to the. plate by means of ascrew-threaded fitting 162.

' Before describing the modified vacuum plate150; in detail referenceshould be made to some of the problems which are overcome by using theimproved plate construction in a casting apparatus. It has been found inpractice that the vacuum hose extending between the clamping plate 150and the vacuum pump often becomes restricted or entirely obstructed withsolid materials such that the vacuum action at the clamping plate iseffectively shut oif before all of the occluded gases and the like havebeen withdrawn from the mold cavities. That is, solid materials aredrawn from the mold outwardly through the plate opening and into thevacuum line with theresult that the latter becomes plugged and theeffective application of vacuum to the mold iscut ofif.

These solid materials often comprise particles of the mold itself, suchas granulesof sand, gypsum, or other mold material which may be presentin a loose state on the surface of the mold or may result from somecrumbling of the soft mold material at its surface. Sometimes thesealing knife edges 158, around the periphery of the clamping plate tendto dislodge particles of mold material from the mold surface.

. The most troublesome type of solid material which may clog the vacuumpassages is the molten metal itself which is being cast. Occasionally amold cavity is positioned very close (perhapsMr inch) to the outersurface of the mold such that a fine crack or void in the thin mold wallwill permit the vacuum to break the wall. If this occurs, some of themolten metal being poured into the mold cavities is invariably drawnthrough the break in the mold wall and into the interconnected vacuumpassages 156 defined by the plate clamping feet 152. Since the moltenmetal solidifies within the vacuum hose and often within the pump itselfit is necessary to completely disassemble and clean the component partsof the pump, a laborious and time consuming task.

, The use of conventional filtering means on the vacuum lines to protectthe vacuum pump has been found to be ineffective since these veryquickly become clogged with the molten meltal or mold particles and thuscut off vacuum action. In any event such filters must be placed in thevacuum hose or line at some point between the clamping plate and thepump such that the portion of the vacuum line adjacent the clampingplate is still subject to Plugging- In carrying out that aspect of theinvention shown in Figs. 18-20 of the drawings, the illustrative moldclamping plate 150 is provided with means surrounding the vacuum opening160 for preventing passage of any solid materials into the vacuum hoseor pump while yet assuring free passage of gases through the opening 160so that occluded gases within the mold cavities may be quickly andcompletely removed therethrough. In this instance the means comprises anapproximately square pad 166 integral with the plate 150 and surroundingthe plate opening 160 and defined by certain of the interconnectedpassages 156, and a porous disc 168 covering the plate opening 160 andshouldered within the pad 166 such that it is interposed between theplate and the mold surface 154 (see Fig. 20) during casting.

As will be seen from Fig. 18 which shows the plate without the porousdisc 168 in place, the pad 166 comprises a plurality of mold engagingfeet 170 which cover substantially the entire area of the pad except forthe center thereof through which the plate opening passes. The moldengaging feet are defined by a plurality of pad grooves 172 which extendradially outwardly over the mold engaging surface of the pad from thecentral plate opening 160 and thereby provide communication between theinterconnected passages 156 and the opening 160.

A counterbore 173 somewhat larger than the diameter of the plate opening160 is provided in the center of the pad 166 in order to provide ashoulder 174 for reception ofthe porous disc 168 which is preferably offlat cylineg-ssatosr 1.1 drical-shape=As-will be seenfmm-FigQ 20 thedepth of the counterbore 173 from the surface of the mold enga1gagainstthe mold surface.

entry ofthe disc 168- therein andremovaltherefron'r.

The disc 168 is thus a wedge-fit when in-place -within the counterbore173. Y

Various materials ofconstruction maybe used for the disc or'waf'er 168"so long as the resultingmaterial is.

porous andresistant to whatever high temperature-conditions areencountered withthe particular metalsto-be cast. "One satisfactory suchdisc isf'ormed as arefractory material bymixing a small amount :ofasuitable binder,

such as the resin binder manufactured and sold I by the Acme ResinCorporation ofForest'Park, Illinois and designated by themas their No.760' resin, with a suitable coarse grade sand, forming themixture intothedisc shape in a conventional core box, and-then baking the shapeddisc at about 800 F. for an hour-or more. The resulting disc is hard;porous due to elimination of "resin components during baking, andresistant to-most-tem'-- peratures encountered in the casting of metalshapes;

Of:cou-rse other binders can be usedas well} and indeed"thedisc-material may beformed of otherhightemperature I resistantmaterials, such forexample as a suitable sin-- tered metal which has thedesired heat resistant qualities.

The modified plate shown-in Figs. 18-20 has many advantages. 7 firmlybetween the plate opening 160 and the mold surface 154- when the entirecasting apparatus is as-sembled The flat disc 168-is, as noted-above,held 12 porous disc 168-thus permits passage of 'air theretliroughi?while yet providing enough resistance to air flow tq-enablje; it to beheld in place within the plate under-impctuirof the vacuum. V i i lnthe-preferred form of the modified plate there-are; yet otheradvantageous features. Attention is drawn to;- the differenceindepthbetween thepad grooves"172'and'-f the-adjacent interconnectedplate passages 1 56. It will" be observed that the grooves 117 2* arepreferably; consid erably more shallow than (only about one-thirdas-decp in this case) the passages 156. These shallow grooves" 172"communicating between the passages 156 and the porous disc 168 functionin what' mightbe termcdfa; coarsefiltering action as'compared with:therelatively fine-"filtering action through/the disc168; jThis'is'best;

. understood upon aconsideration" of the mechanicsofi and the metal isbeing cast. As will be clearly seenfrom- -Fig. 20, any solid materialssuch as-rnold particles of molten metal which'enter the interconnectedpassages 156 from the mold will. be drawn along those passages totheplate pad 166 and thence through thepadgrooves 172i'until. theparticles engage the outer peripheral edge" surface of the disc 1 68.The solid particles are stopped at. thispoint and'must remain lodgedagainst-theouten edge surface of the disc.

An important feature of' this aspect of the invention is that the flatdisc 168Jin this condition providesabroad filtering area in engagementwith the mold surface 154' such- -that effective vacuum action isexerted upon the inner moldcavities over-the entire fiat area of thedisc: Becauseof the substantial area of flat engagement between the disc168-and the mold 154, thatportion of the moldin contact with the disc isstrengthened againstanycracking or breaking of the mold Walloverthatarea;

Since the mold wall remains intact-over the "area of engagement with thedisc 1 68, and because any loose solid particles from the mold areretained on the edge surface" ofthe disc, there i's-no' substantialimpairment-.of'the: vacuum action being exerted throughthe fiat discsurface upon the-mold cavities. Even in anextreme hypot heti'calisituationin which all of the pad grooves 1-72"-rnight become cloggedwith solid materials, vacuum" would *still be drawn through. theflatcsurface of the di'sc1'68ienga-ging the mold surface.

Another feature of this modified form ofthe-invention concerns theeasewith whichthe filtering means' may be cleaned in between successive usesof theycastingi appw ratus. Upon separation of theclamping-plate150-fron1 the casting apparatus and" discontinuation ofvacuum action, the disc 1'68 drops easily out of the: plate shoulder.

1741-and the solid particles may be easilybrushednway I from-the disc aswell'as from the grooves17-2P'an'dother plate passages. Reassemhlyisaccomplished readily by applying vacuum to the clamping plate 150,placing the the path of flow should molten metal' or mold-particlesbedrawn into the interconnected-vacuum passages 156; Goblets or particlesof such molten-metal are firstdr'awrr along the relatively large anddeep-passages 156-toward.

At this point of entry'of the molten metal particles into V the grooves172 the velocity of the flow of'gasesand... the like from the moldcavities increases substantially in accordance withthe above-mentionedchange in: cross: sectional area of the path'of gas flow such thatachilling action takes place tending to slidify the particles .of moltenmetal. As a result many times the chilledmetalpan ticles, or thesmallerparticles of'mold material, are caught within the confines of thenarrow grooves 17Z'sq that they never reach the porous disc 168; Ofcourse much of the particulate material will traversethepad' grooves 172and be drawn up against the edge surfaces of the disc 168 as describedabove. sectional area of the grooves 172 is invariably considerablygreater than the size of the voids in porous. disc 168 the narrowgrooves provide what'might be termed a. coarse filtering or screeningaction. 7

It is found in practice that this arrangement not'onlyj prevents thevacuum line from plugging up but assures.

the maintenance of a positive vacuum against thesurface of the mold fora sufficient period of time to permit'the occluded gases to be withdrawnfrom the mold cavity.

Thus; while there is still the'possibility that even the 7 While themodified form of" the invention disclosed in Figs. 18-20 of the drawingshas been described as applied to the top plate of a casting apparatusand a plate of rectangular form, the invention is in. no wise so:limited. Anysuitable shape castingv plate may be em: ployed and it" maybe a bottom plate or the like as well.. as the top plate. Similarly theplate pad 166 need not be-square-shaped but may take any suitable formandI-the-.. disc \168need not be cylindrically shaped but maybe formedas a rectangular or square solid or in anyothel; feasible shape.Likewise this aspect of the invention may be used in permanent moldssuch as cast iron .or the like used for casting various alloys andaluminum as well as non.

permanent types. In this application avacuum opening is provided on theinner wall. of the permanent mold, with a suitable'recesssurroundingthe. opening; themoldfcoma prising-for example .a heavy walledcast ironcylinder... about 10 inches in'diameterand" perhaps Ginches deep,

Since the: cross-. V

13 and the recess being sized and shaped to receive therein a porousdisc of suitable contour and of the character described above. Theposition of the disc within the mold ary 25, 195 6, now abandoned, whichis in turn a continua- I tion of my now abandoned application Serial No.379,210

filed September 9, 1953. s V

I claim as my invention: f M 1. A casting apparatus comprising, incombination, a

mold formed of porous material defining a cavity for the reception ofthe material to be cast, a plate having a plurality ofinterconnectedpassages formed in one face thereof and defining a plurality of spacedfeet engageable with said mold, said mold and said plate defining spacedpassages therebetween, said plate having an opening therein adapted forconnection with evacuating means and including on said face thereof apad surrounding said opening and having a depth substantially the sameas the depth of said spaced passages, a counterbore on said plate facewithin said pad and surrounding said plate opening, said pad havinggrooves therein communicating between said spaced passages and saidplate opening and dividing said pad into a plurality of feet forengagement with the juxtaposed mold surface, means for applying a vacuumto said plate through said plate openi'ng'whereby vacuum is transmittedthrough said spaced passages to the exterior surface of the mold andindirectiy to said mold cavity through the mold walls defining the samefor effecting removal of gases from the mold cavity, said pad grooveshaving a depth substantially less than the depth of said spaced passageswhereby flow of gases from said mold cavity to said plate opening isrestricted, and a porous disc within said counterbore disposed inparallel relationship to the interface between said plate and said moldand being of a sufficient thickness to locate the outer surface of thedisc in coplanar relationship with the mold bearing surface of saidspaced feet so that the disc is held in firm engagement with thecontiguous area of the mold surface whereby the disc permits passagethere- 'through of gases being evacuated from the mold cavity butpositively prevents passage into the plate opening of any solidparticles that might otherwise obstruct said opening.

2. A casting apparatus comprising, in combination, a mold formed ofporous material defining a cavity for the reception of the material tobe cast, a plate having a plurality of interconnected passages formed inone face thereof and defining a plurality of spaced feet engageable withsaid mold, said mold and said plate defining spaced passagestherebetween, said plate having an opening therein adapted forconnection with evacuating means and including on said face thereof apad surrounding said opening and having a depth substantially the sameas the depth of said spaced passages, a counterbore on said plate facewithin said pad and surrounding said plate opening, said pad havinggrooves therein communicating between said spaced passages and saidplate opening and dividing said pad into a plurality of feet forengagement with the juxtaposed mold surface, means for applying a vacuumto said plate through said plate opening whereby vacuum is transmittedthrough said spaced passages to the exterior surface of the mold andindirectly to said mold cavity through the mold walls defining the samefor effecting removal of gases from the mold cavity, said pad groovesextending radially outward from said plate opening and having a narrowdepth as compared with the depth of said passages whereby flow of gasesfrom said mold cavity to said plate opening is restricted, and a porousdisc within said counterbore disposed in parallel relationship to theinterface between said'plate and said mold and being of a sufiicientthickness to locate the outer surface of the disc in coplanarrelationship with the mold bearing surface of said spaced feet so thatthe disc is held in firm engagement with the contiguous area of the moldsurface whereby the disc permits passage therethrough of gases beingevacuated from the mold cavity but positively prevents passage into theplate opening of any solid particles that might otherwise obstruct saidopening.

3. A casting apparatus comprising, in combination, a mold formed ofporous material defining a cavity for the reception of the material tobe cast, a plate having a plurality of interconnected passages formed inone face thereof and defining a plurality of spaced feet engageable withsaid mold, said mold and said plate defining spaced passagestherebetween, said 'plate having an opening therein adapted forconnection with evacuating means and including on said face thereof apad surrounding said opening and having a depth substantially the sameas the depth of said spaced passages, a counterbore on said plate facewithin said pad and surrounding said plate opening, said pad havinggrooves therein communicating between said spaced passages and saidplate opening and dividing said pad into a plurality of feet forengagement with the juxtaposed mold surface, means for applying a vacuumto said plate through said plate opening whereby vacuum is transmittedthrough said spaced passages to the exterior surface of the mold andindirectly to said mold cavity through the mold walls defining the samefor effecting removal of gases from the mold cavity, and a porous discwithin said counterbore disposed inparallel relationship to theinterface between said plate and said mold and being of a sufiicientthickness to locate the outer surface of the disc in coplanarrelationship with the mold bearing surface of said spaced feet so thatthe disc is held in firm engagement with the contiguous area of the moldsurface whereby the disc permits passage therethrough of gases beingevacuated from the mold cavity but positively prevents passage into theplate opening of any solid particles that might otherwise obstruct saidopening, said pad grooves terminating adjacent said plate openingagainst the peripheral edge surfaces of said porous disc so that anysolid particles accumulate along these edge surfaces whereby the flatsurface of the disc lying in the plane of the mold surface remains freeand unobstructed to passage of gases therethrough.

4. A casting apparatus comprising, in combination, a mold formed ofporous material defining a cavity for the reception of the material tobe cast, a plate having a plurality of interconnected passages formed inone face thereof and defining a plurality of spaced feet engageable withsaid mold, said mold and said plate defining spaced passagestherebetween, said plate having an opening therein adapted forconnection with evacuating means and including on said face thereof apad surrounding said opening and having a depth substantially the sameas the depth of said spaced passages, a counterbore on said plate facewithin said pad and surrounding said plate opening, said pad havinggrooves therein communicating between said spaced passages and saidplate opening and dividing said pad into a plurality of feet forengagement with the juxtaposed mold surface, means for applying a vacuumto said plate through said plate opening whereby vacuum is transmittedthrough said spaced passages to the exterior surface of the mold andindirectly to said mold cavity through the mold walls defining the samefor effecting removal of gases from the mold cavity, said pad grooveshaving a depth substantially less than the depth of said spaced passageswhereby flow of gases from said mold cavity to said plate opening isrestricted, and a '15 mold 'bearing lsurface of said spaced feet so thatthe disc is held in firm engagement with the contiguousareaflof the moldsurfacelwhereby the disc permits passage therethrough of gases beingevacuated from the mold cavity but positively prevents passage into theplate openingwof; any solid particles that might otherwise obstructsaid' mold'forrned of porous material defining a cavity forthe 7reception oflthe material to be cast, a support for the mold, a platehaving a plurality of interconnected 'passages formed in one facethereof and defining a plurality of.spaced feet engageable with saidmold opposite said support, means for clamping said plate against saidmold, said mold and said plate defining spaced passages there'- between,a perforated member entirely surrounding the exposed mold portions forsustaining the form thereof and" permitting-passage of air therethrough,said plate having an opening therein adapted for connection with evacuating means and including on said face thereof a pad surrounding saidopening and having a depth substantially the same as the depth of saidspaced passages, a counterbore on said plate face within said pad andsurrounding said plate opening, said pad having grooves thereincommunicating between said spaced passages and said plate opening anddividing said pad into a plurality of feet for engagement with thejuxtaposed mold surface, means for.

applying avacuum to said plate through said plate open-j ingwherebyvacuum is transmitted through said spaced. passages to the exteriorsurface of'the mold andlindirectly to said mold cavity through the moldwalls defining the same for effecting removal of gases from the moldcavity; and for drawing air into the mold'through said perforated" moldsupporting member, said pad grooves having fa. depth substantially lessthan the depth of r said 'spacedt'i passages whereby flow of gases fromsaid mold cavity to said plate opening is restricted, andia porousdiscw'ithinr said counterbore disposed in parallel relationship to theinterface between said plate and "said mold and being off. a suflicientthickness to locate the oute'r surface ofthe,

disc in coplanar relationship with the moldb'earin'gfsup face of saidspaced feetso that the disc is held in firm engagement with thecontiguous area of the;moldfslirface whereby the.discpermitspassage-therethrough off'gasesj being evacuated from themold cavity butpositivelyprei vents passage into the plate opening of any s'olidparticles" that might otherwise obstruct said opening.

References Cited in' the file of this patent UNITE-D STATES-PATENTS,

1,031305- West' July-2, 1912' 133 62182 1-,ss'1,4=4-s 2-,1'9"s;497;'2,209,081 23220316;

Wetherby t June 6, 1911 Moore" Feb. 22; T921 1 Lake Mar. 3'1, I925

